Amplifying system



' March 3, 1931. T. H. KINMAN. 1,795,172

AMPLIFYING SYSTEM Filed Sept. 21, 1928 Inventor Thomas.H-Kinma.n, u WYMHts Attorney- Patented Mar. 3, 1931 (UNITED STATES PA EI FFCE THOMAsH.KINMAN, or BILTON, RUGBY, ENGLAND, ASSIGNOR 'ro GENERAL ELECTRICCOMPANY, A CORPORATION OF NEW YORK- V 'AMPLIFYING SYSTEM,

Application filed September 21, 1928, Serial No The present inventionrelates to amplifying systems which include electric discharge devicesand are particularly intended for the amplification of high frequencyelectric oscillations.

The Object ofthe invention is to simplify.

the operations necessary for the adjustment of a high frequencyamplifier so that it may be especially suitable for incorporation in a10 radio receiving system adapted to receive alternatively on a numberof specified wave lengths or frequency channels.

In accordance with the invention, an amplifying system of theabove-named type for 16 high frequency oscillations is renderedsimultaneously selective to oscillations of two or more predeterminedfrequencies. In order to obtain this result, the anode circuit of one ormore of the electric discharge de- 20 vices employed,- which may beordinary receiving vacuum tubes, for example, is 'ren dered selective tothe predetermined frequencies'by including therein a plurality ofcircuits tuned to the various frequencies it is desiredto select, theconstants and arrange ment of each tuned circuit being such that itaffords a negligible impedance to oscillations of the frequencies towhich the other circuits are tuned.

In 7 carrying the invention into effect, I preferably employtubes Of thetype now commonly/ known as screen-grid tubes, that is to say. tubeshaving the usual cathode, anode andcontrol grid and'provided, inaddition, with a screen grid located between the control grid and theanode, the purpose of which is to eliminate the inter-electrode capacitywhich would otherwise exist between the control grid and the anode. Twoor more inductances connected in series or in parallel in the anodecircuit of the tube are tuned to the frequencies itisi particularlydesired to amplify, The tuned circuits are so designed that whicheverone of the tuned circuits offers a high impedance to that frequency,:while the remaining tuned circuits offer littleor no impedance to thatfrequency. Thatis to say, the remaining tuned circuits freely passoscillations of a frequency other than that to which they are with, anantenna or like receiving device for frequency is being amplified,

. 307,474, and'in Great Britain October 10, i927.

specifically tuned. By a suitable coupling device, the voltagepulsations set up across the circuit tuned to the frequency beingamplified is transferred to-the grid of the next tube in the system,which may be another amplifying tube, or means arranged to 'de- I tectthehigh frequency oscillations. I v

. The input circuit of the first tube of the system is preferablycoupled to, or associated the high frequency oscillations, the antennaorinput circuit being tuned to the frequency it-is desired to receiveand to amplify selectively. V p p p The arrangement in accordance withthe present invention although not limited there'- to, is particularlyadapted for use with an antenna, Or'like receiving device, arranged toreceiveon alternative wave lengths in the manner described in mycopending application, Serial NO.219,088, filed September 12, 1927. Thetuned circuits situated in the anode circuits of the tubes are thentuned to the same-frequencies as those to which the antenna or inputcircuit-is tuned,and when oscillations of either of the selectedfrequencies'are received, they are selectively amplified in the systemlAny adjustment is unnecessary other than those adjustments made when thecircuit arrangement is first assembled. V

My invention will be better understood vfrom the following descriptionwhen confication stages arranged in accordance with the invention andutilizing electric discharge devices of the screened grid vacuum tubetype. a

Referring to the drawing, a signal receiv-. ing device 5, provided inthe present example with an inductance 6 coupled with an antenna 7 by acoil 8, is connected to thefilament and control grid of the first tube9, and

isshunted by two condenserslO and 11 in parallel, thelcondenser llhavinga switch 12 arranged to connect and disconnect it. When the aforesaidcondenser 11 is disconnected, the remaining condenser 10 tunesinductance 6 to one of the frequencies it is desired to receive wherebythe signal receiving device is responsive to that frequency or signalsof that frequency. On connecting in the condenser 11 the increasedcapacity obtained is of such value as to tune inductance 6 toth-eotherfrequency it is desired to two tuned circuits 18-14 and- 1516 in series,each consisting of an inductance and capacity in parallel, 13 and 15being the inductances and 14 and 16 their respective tuning; capacities.The resonant frequencies of these two tunedcircuits correspondrespectively with the frequencies to which the signal receiving deviceis capable of being tuned. These frequencies should preferably beseparated. by a fairly wide margin, whereby a response to a band offrequencies isprevented, and when employed for the reception ofbroadcasting, may correspond with the frequencies of a main station andanother high power, long wave station, for example. The constants of thetuned circuits-in: the anodecircuit are so: arranged that at thefrequency to which one of them is tuned, the condenser of the remainingtuned circuit constitutes a low impedance for that frequency, and viceversa. The potential variations set up at the terminals of the tunedcircuits are transferred from the high potential end of the anodecircuit tothegricl of the next tube 17, which may be a detector oranother amplifier, but which in the arrangement shown is: a secondamplifier, through the usual single coupling capacity 18,. and aresistor 19' is provided for applying ab-ias ing potential to the gridof tube l'Z. The connectionfrom the end of the tun-ed circuits 15-16,remote from the anode, to the anode through a second coupling condenser26, and a grid biasing or load resistor 27 is connected across theoutput circuit which is indicated at 28.

The coupling between each of the tuned anode circuits and the succeedingtube or device may be: obtained in other ways, for example, throughtuned circuits similarly as sociated in the grid circuit of thefollowing tube, which are coupled respectively to the tuned circuitssituated in the anode circuit of the preceding valve.

Likewise one skilled in the art will readily appreciatethatthe tunedanode circuits may similarly be arranged in parallel, instead of inseries as described, one tuning condenser only being employed to tunethe two inductances. Similarly, in the series: arrangement described,the tuning condenser for the shorter wave may be eliminated with. properdesign of. the inductance- Thus ind uctances 13- and 22 may be wound: inthe form of aperiodic radio-frequency chokes, so that they will respondto a definite or. predetermined wave band, such asthebroadcastband from260- to 500- meters, while 15 24 may be tuned by fixed or variablecondensers I6- and 2:5; to any longer wavelength, as previouslydescribed. I

It has been: found that the use of screengri-d tubes assists in theapplication and successful operation: of the amplifier, although it isdesiredto: point out that the benefits of the invention can be obtainedwith other suitable tubes such: asthe more usual. three-electtrocle-type..

It is desirablethateach stage of high frequency amplification, with its;associated circuits, should be effectively screened-i from its neighborall external influences.- This may be done by suitable metal enclosuresvor shields. now commonly known and used.

A: receiver or amplifier arranged in accordance with the invention isadvantageous inas much as reception and amplification is possible on aplurality of alternative wave lengths without any adjustment other thantheoperation of a simple switching device, which is" incorporated in theinput or other tuned receiving circuit, as-herei-nbefore referred to. Noadjustmen'tof the amplifier itself is necessary.

It will also be evident that, although the provision of two tunedcircuits in each anode circuit of the tube has been specificallyreferred to in the present example, more than two tuned circuits: may beemployed if desired, thereby rendering the arrangement selective to morethan two predetermined frequencies;

hat I claim as new and desire tosecure by Letters Patent of the UnitedStates, is-:

1. Ina high frequency signal amplifying system employing a plurality ofelectric dis charge devices, a plurality of circuits tuned to differentpredetermined frequencies and included in a single anode circuit of oneof said devices, said frequencies being separated to prevent band passtuning in said circuit, the constants of each tuned circuit being suchthat it produces a negligible impedance drop when subjected tooscillations of frequencies to which the other circuits are tuned andproduces a high impedance drop when subjected to the frequency to whichit is tuned, a single coupling means connected with the high potentialend of the anode circuit and with the control electrode of a secondelectric dis-- charge device, and selector means for selectivelyintroducing into said system a signal of any one of said predeterminedfrequencies.

2. In a radio frequency amplifier including two electric dischargedevices, the combination of a signal receiving device, means forselectively tuning said receiving device separately to each of aplurality of relatively widely separated predetermined frequencies, anda single tuned circuit introduced between said electric dischargedevices and connected with the anode of the one and the grid of.

the other, said circuit being arranged to respond to any quencies andincluding a series of tuned inductance units each tuned to a differentone of said predetermined frequencies.

In witness whereof, I have hereunto set my hand this fourth day ofSeptember, 1928.

THOMAS H. ICINMAN.

of said predetermined fre-'

